1. Field of the Invention
The present invention relates to a method for channel coding 7 input data bits into 13 channel data bits and channel decoding the channel-coded 13 channel data bits into the prior-to-channel-coding 7 data bits, using a run-length-limited (RLL) (2,25) code during transmission and recording/reproduction of digital data.
2. Description of the Related Art
Channel coding converts digital data so that it is adapted to the feature of a transmission medium or a recording medium, in order to transmit or record the digital data under optimal conditions, which is also called channel modulation. The RLL channel coding method is chiefly used as a channel coding method for recording digital data on a recording medium such as an optical disk. The RLL channel coding method channel codes m-bit input data into n-bit channel data, so that the length of a successive zero run satisfies a (d,k) condition, which is expressed as (d,k,m,n;l) or RLL(d,k). Here, d denotes the minimum length of the successive zero run (hereinafter, referred to as minimum run length), k denotes the maximum length of the successive zero run (hereinafter, referred to as maximum run length), m denotes the number of minimum unit input bits, and n denotes the number of minimum unit channel bits. Also, when digital data is variably input, the number of maximum unit input bits is denoted by l. For example, when input data is varied among m, 2 m, 3 m and 4 m, l is 4 m. A recording density ratio (DR) of the RLL channel coding method is defined as ##EQU1##
Here, ##EQU2##
represents a conversion ratio when m-bit input data is converted into n-bit channel data, and (d+1) represents a minimum interval of time. Thus, the conversion ratio and/or the minimum interval of time should be increased in order to increase a recording density ratio.
Different types of the RLL channel coding method are an Eight-To-Fourteen (EMF) method, an RLL(2,7) method, an RLL(1,7) method, and an EFM-plus method. The EFM method where (d,k,m,n) is (2,10,8,17) is a channel coding method proposed by Philips Co. Ltd. which is chiefly used in a compact disk (CD). The EFM method converts 8-bit input data into 14-bit channel data. However, since the EFM method additionally requires three merging bits for controlling a digital sum value (DSV), the conversion ratio is decreased to ##EQU3##
the minimum interval of time becomes 3T, and the recording density ratio becomes 1.41. Meanwhile, the EFM method is not appropriate for a high-density optical disk requiring a real-time processing because of a large size of a code book for channel coding and decoding. In the RLL(2,7) method where (d,k,m,n) is (2,7,1,2), the conversion ratio is 0.5, the minimum interval of time becomes 3T, and the recording density ratio becomes 1.5, which is chiefly used in a magneto-optical disk (MOD). In the RLL(1,7) method where (d,k,m,n) is (1,7,2,3), the conversion ratio is 0.67, the minimum interval of time becomes 2T, and the recording density ratio becomes 1.33, which is chiefly used in a 4-times capacity (4.times.) magneto-optical disk (4.times.MOD). In the EFM-plus method improving the EFM method where (d,k,m,n) is (2,10,8,16), the conversion ratio is 0.5, the minimum interval of time becomes 3T, and the recording density ratio becomes 1.5, which is chiefly used in a digital versatile disk (DVD). The above-described conventional RLL channel coding methods are summarized in the following Table 1.
TABLE 1 modulation type EFM RLL(2, 7) RLL(1, 7) EFM-plus (d, k, m, n) (2, 10, 8, 17) (2, 7, 1, 2) (1, 7, 2, 3) (2, 10, 8, 16) conversion 0.47 0.5 0.67 0.5 ratio recording 1.41 1.5 1.33 1.5 density ratio application CD MOD 4X MOD DVD field
However, when the minimum run length is 2 among the above channel coding methods, 16 or 17 channel data bits are required with respect to 8 input data bits. Thus, the conversion ratio is lowered and the recording density ratio is not improved. Also, in the RLL(1,7) method where the minimum run length is 1, 8 input data bits are converted into 12 channel data bits, with a result that the conversion ratio is increased. However, the minimum interval of time is 2T and the recording density ratio is only about 1.33, which causes a lower recording density ratio than those of the other methods.